Pyromellitic dianhydride (which may hereafter be referred to as “PMDA”) is often used in a production apparatus for producing semiconductors, solar cells, and the like, or in research equipment for developing new materials, as a material for forming semiconductor films that are demanded to be highly pure products. PMDA is often used in a gas phase by being heated and sublimated at a predetermined temperature, and is sublimated and transported by an inert gas having a low reactivity and a high stability such as a rare gas such as helium or argon, so as to be supplied to the above production apparatus and consumed.
In particular, when PMDA is used as a raw material for a polyimide resin having a high heat resistance, a cross-linking agent for foamed polyester, a special plasticizer, or the like, highly pure pyromellitic dianhydride is demanded, and various production methods are proposed. For example,
there is a method for producing a pyromellitic dianhydride comprising a step of thermally dehydrating crude pyromellitic acid in the absence of acetic anhydride to convert 50.0 to 99.5 wt % of the pyromellitic acid into pyromellitic dianhydride and affording a reaction mixture containing at least pyromellitic acid and pyromellitic dianhydride and a step of thermally dehydrating the reaction mixture in the presence of acetic anhydride (See, for example, JP-A-2013-006856).
In addition, as a method for supplying such highly pure pyromellitic dianhydride, various supplying methods and supplying apparatus are proposed due to the special handling properties of the pyromellitic dianhydride. For example, there is a construction example of an evaporator delivery system 110, as shown in FIGS. 10A and 10B, having numerous containers that provide an enlarged surface area for evaporation of liquid and solid materials such as liquid and solid source reagents used in the chemical vapor deposition (CVD) method, the atomic layer chemical vapor deposition (ALCVD) method, and the ion injection method (See, for example, JP-A-2006-503178). In an ampule 112, a plurality of vertically stacked containers 122 including a bottom 114 and a side wall 116 that form an inner chamber are placed in an inner chamber of the ampule. The stacked containers are separable from each other and removable from the ampoule for easy cleaning and refilling. An internal carrier gas member 123 is placed in the ampule, and this internal carrier gas member 123 is connected (welded) to a carrier gas inlet 120 to guide a carrier gas to the bottom of the inner chamber and under the lowermost container of the vertically stacked containers. The internal carrier gas member 123 passes through each of a container cavity 127 and a container bottom 124. The individual containers 122 are each provided with the bottom 124 and a side wall 126, so as to form a container cavity 127 for placing preferable source materials 128. Each of the individual containers includes a plurality of protrusions 130, and each protrusion includes a passageway 132 along which the carrier gas moves by passing through the protrusion (See paragraphs 0018 to 0023 of JP-A-2006-503178). Here, reference numeral 138 denotes an O-ring for sealing and reference numeral 140 denotes a gas outlet valve.